Biology subjects

Sarangi, R.

Publications and source records attributed to Sarangi, R..

9 recordsLinked to original sources

bioRxiv2026

A Binuclear Cluster Supports Functional Asymmetry in Dark-Operative Protochlorophyllide Reductase

Many photosynthetic bacteria rely on the nitrogenase-like dark-operative protochlorophyllide oxidoreductase (DPOR) to sustain (bacterio)chlorophyll synthesis in the dark. DPOR couples ATP hydrolysis to electron transfer from a reducing component (L-protein) to a catalytic component (NB-protein) that reduces protochlorophyllide. NB-protein is an 2{beta}2 heterotetramer, and each heterodimeric half contains an active site and a [Fe4S4] cluster. Although the two halves are identical, they react sequentially rather than in parallel. How the two halves communicate has remained unknown. Here we show, using Cu K-edge x-ray absorption spectroscopy and cryo-EM, that the NB-protein tetramer interface holds a binuclear, sulfur-bridged [Cu2S2] cluster. Each Cu is reduced and three-coordinate, with short Cu-S and Cu-Cu distances (2.26 and 2.62 &Aring). Mutagenesis excludes the nearest cysteine as the bridging ligand, supporting inorganic sulfide as the most likely sulfur donor. To our knowledge, this is the first sulfide-bridged dicopper cluster identified in a protein. The cluster is conserved in three purple non-sulfur bacteria and connects the BchB C-terminal helices that contact opposing active sites. Loss of Cu abolishes DPOR activity and asymmetric L-protein binding without disturbing overall fold. We propose that the cluster relays substrate-binding information between active sites, suggesting a metal-mediated mechanism for cooperativity in nitrogenase-like enzymes.

biochemistry↗

bioRxiv2026

Hydrogen sulfide dynamically upregulates copper uptake and localization

The reactivity of copper, an essential micronutrient that undergoes facile cycling between Cu1+ and Cu2+ redox states, is carefully controlled within the confines of protein binding sites, and by sequestration in storage vesicles, or harnessed to kill pathogens by active pumping of Cu1+ into phagosomes. We have discovered that hydrogen sulfide, a signaling metabolite generated in copious quantities at the host-microbiome interface, upregulates Cu accumulation in diffusely dispersed puncta across the cell, as visualized by X-ray fluorescence microscopy. The Cu is predominantly in the Cu2+ state with oxygen/nitrogen ligands. Cu import occurs via the non- canonical ZNT1 transporter, while export, following sulfide withdrawal, is ATP7A-dependent. Cu accumulates at the apices of colon crypts in a mouse model of elevated sulfide exposure due to SQOR deficiency in the intestinal epithelium, establishing in vivo relevance. Our study reveals that sulfide is a dynamic regulator of the Cu pool, stimulating Cu2+ influx into highly concentrated puncta.

cell biology↗

bioRxiv2026

Ferrosome Organelles Spatially Insulate a Redox-Active Ferrous Phosphate Biomineral from Cytosolic ROS Chemistry

Ferrosomes are recently discovered lipid-bound bacterial organelles that store iron as iron-phosphate biominerals, yet the chemical nature and physiological consequences of ferrosome-stored iron remain poorly understood. Here, we combined X-ray absorption spectroscopy (XAS), electron microscopy, inductively coupled plasma mass spectrometry (ICP-MS), and physiological analyses to characterize ferrosome iron in Clostridioides difficile. XAS analysis of isolated ferrosomes revealed an amorphous iron-phosphate biomineral containing mixed Fe(II)/Fe(III), consistent with partial oxidation during aerobic isolation. In contrast, whole-cell XAS of intact anaerobically maintained cells demonstrated that ferrosomes predominantly contain a structurally disordered ferrous phosphate biomineral with local Fe-O-P coordination features similar to those of vivianite. Upon air exposure, this ferrous biomineral rapidly oxidized to a ferric phosphate-like state, revealing a highly oxygen-sensitive iron-storage phase. Despite containing abundant redox-active Fe(II), ferrosome-stored iron contributed minimally to the cytosolic labile iron pool. Consistent with this observation, isolated ferrosomes exhibited little ROS-generating activity, and ferrosome-overproducing cells displayed no substantial increase in sensitivity to oxygen, peroxide, or paraquat stress relative to ferrosome-deficient controls. Together, these results establish ferrosomes as iron-storage organelles that sequester redox-active Fe(II) in a mineralized ferrous phosphate phase, limiting its participation in cytosolic ROS chemistry and providing a mechanism for the safe storage of reactive iron. Significance StatementIron is essential for life but can also damage cells because ferrous iron drives oxidative stress. How cells store large amounts of ferrous iron while limiting toxicity therefore remains a fundamental biological question. Ferrosomes are recently discovered bacterial organelles that store iron as iron-phosphate biominerals, but the chemical nature and physiological consequences of ferrosome-associated iron remained unknown. Using Fe K-edge X-ray absorption spectroscopy, we show that ferrosomes in Clostridioides difficile contain a redox-sensitive ferrous phosphate biomineral. Physiological analyses demonstrate that this iron is largely inaccessible to cytosolic reactive oxygen species (ROS) chemistry. These findings reveal that bacteria can combine biomineralization and subcellular compartmentalization to maintain large intracellular iron reservoirs while limiting iron-dependent oxidative damage.

microbiology↗

bioRxiv2026

Zero-shot design of a de novo metalloenzyme

The de novo design of enzymes remains a central challenge, requiring consideration of catalytic mechanism and optimization across biochemical and biophysical criteria. Here we present dEVA (design by EVolutionary Algorithm), a multi-objective protein design framework built on principles drawn from evolutionary biology. We apply dEVA to the zero-shot, de novo design of metalloenzymes by optimizing the coordination sphere of catalytic metals. We characterize a bizinc metalloenzyme that exhibits promiscuous hydrolytic activity towards both phosphomonoesters and phosphodiesters. This design achieves a rate enhancement ((kcat/KM)/kw) up to 3 x 1013, comparable to characterized natural phosphatases. dEVA offers a general and modular strategy for the programmable design of protein function without dependence on natural templates or evolutionary information.

biochemistry↗

bioRxiv2026

Use of Substrate Analogues and X-ray spectroscopy Reveals an all Ferrous C-Cluster in CO Dehydrogenase

Carbon monoxide (CO) dehydrogenase (CODH) plays a key role in prokaryotic one-carbon metabolism by detoxifying CO and by driving CO2 reduction coupled to ATP production in the Wood-Ljungdahl Pathway. Here we focus on a Ni-Fe CODH (CODH-II), with an active site C-cluster, which is a [NiFe4S4] cluster arranged as a [NiFe3S4] subcluster with an additional, unique pendant Fe, e.g., [Fe3S4-Feu]. It catalyzes the reversible reduction of CO2 to CO without the requirement for an overpotential and with insignificant proton reduction. The redox states associated with catalysis are defined as Cred1 and Cred2. Despite crystal structures with near 1.0 A resolution, it has been a long-standing question where the electrons in these catalytically relevant redox states are stored within the C cluster. Using X-ray absorption spectroscopy (XAS), EPR, and substrate-analogue binding measurements, we clarify the electronic structure of these catalytically active states in addition to the resting state of CODH. We rule out recent postulates that catalysis involves a Ni0 state, a metal-metal bond, or a hydride intermediate. We reveal that CODH rests in the diamagnetic Cox form, which contains Ni2+ and an oxidized [Fe3S4-Feu]2+ cluster. Then, the C-cluster undergoes reductive activation on Fe to form paramagnetic Cred1, which binds CO and analog cyanide. Generation of Cred2, which binds CO2 and its analog cyanate, involves two sequential valence-localized electron transfers, generating Ni1+ and then [Fe3S4-Feu], forming an all-ferrous cluster. Our work sheds light on how CODH avoids the thermodynamically unfavorable generation of a CO2 radical anion intermediate formed in other catalytic systems by stabilizing electron density in the heterometallic C-cluster. We also highlight the importance of high-resolution XAS and use of substrate analogs to reveal the sequential, valence-localized electron transfers that occur during redox-dependent CODH catalysis. TOC Figure O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=93 SRC="FIGDIR/small/700957v1_ufig1.gif" ALT="Figure 1"> View larger version (21K): org.highwire.dtl.DTLVardef@1e8d3caorg.highwire.dtl.DTLVardef@a89cc9org.highwire.dtl.DTLVardef@1cd569dorg.highwire.dtl.DTLVardef@1f1668c_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

bioRxiv2025

Structure of active methyl-CoM reductase, Earth's main methane producer

Our work reveals the structure of the active state of Methyl-Coenzyme M Reductase (MCR), the key and rate-limiting enzyme in biological methane formation. We find large differences between the active Ni(I) and inactive Ni(II) proteins and provide insight into how nature makes and breaks the C-H bond of methane. The Ni(II)-F430 center in inactive MCR contains four planar nitrogen ligands, a lower axial glutamine oxo, and an upper axial thiolate. The Ni(I)-enzyme replaces the axial ligands with a single water. The one-electron redox change results in movement of the Ni ion and upward swing of the {beta}-lactam ring in the tetrapyrrole coupled to a domino-like protein quake through second sphere residues, inter-subunit interactions, a substrate tunnel, affecting even the dimensions of the unit cell. These structural changes lead Ni(I)-MCR to release a charge clamp that, in the Ni(II) state, locks down substrate Coenzyme B. Determining the Ni(I)-MCR structure required development of rigorous anaerobic crystallographic techniques. Validation of the MCR redox state was accomplished by in-line and parallel spectroscopic and unit cell analyses. This structure has large implications for developing technologies to limit methane emissions and efficiently produce biofuels. Methodology described here will enhance structural biology for other oxygen-sensitive enzymes.

biochemistry↗

bioRxiv2023

Inferring B-cell derived T-cell receptor induced multi epitope-based vaccine candidate against enterovirus 71 (EV 71): A reverse vaccinology approach.

In addition to Coxsackie virus (CV), another pathogen that causes Hand-foot and mouth disease (HFMD), Enterovirus 71 (EV 71) is currently regarded as an increasing neurotropic virus in Asia and can cause severe complications in paediatric patients with blister like sores or rashes on the hand, feet and mouth. Not withstanding the significant burden of the disease, few treatments are currently available, and there is no authorised vaccine available for the disease prevention. Several vaccinations based on attenuated and inactivated vaccines have previously been identified, however they become worthless over time owing to changes in the viral genome. As a result, the goal of the study is to create an immunoinformatics and reverse vaccinology pipeline for predicting a multi epitope vaccine. A novel vaccine construct using B-cell derived T-cell epitopes from the virulent polyprotein and found the induction of possible immune response, in order to boost the immune system, aBeta-defensin 1 preproprotein adjuvant with EAAAK linker was added at the N-terminal end of the vaccine sequence. The immunogenicity of the designed, refined, and verified prospective 3D- structure of multi-epitope vaccine was found to be quite high with non-allergen, and antigenic property. The vaccine candidates bound to the TLR-3 in a molecular docking analysis and the efficacy of the potential vaccine to generate a strong immune response was assessed by means of an in silico immunological simulation. Computational analysis has shown that the proposed multi epitope vaccine possibility safe for use in humans and elicit an immune response, making it a promising tool against HFMD viral genome.

immunology↗

bioRxiv2023

Genome-wide mining and comparative analysis of microsatellite markers from Orientia tsutsugamushi genomes

Microsatellite markers, otherwise known as the simple sequence repeats (SSRs), are being used for molecular identification and characterization as well as estimation of evolution pattern of the organism due to their high polymorphic nature. These are tandemly repeated sequences observed almost all organisms and differentially distributed across the genome. Although the primary genome information of Orientia tsutsugamushi (OT) suggested the repeats hold the 40% entire of its genome, but lack of characteristic of this repeats increase our interest to study more about it. Thus we investigated a genome-wide presence of microsatellites within nine complete genomes within OT and analyzed their distribution pattern, composition and complexity. The in-silico study revealed the genome of OT enrich with microsatellites having a total of 126187 SSR and 10374 cSSR throughout the genome from which 70% and 30% represented within the coding and non coding region respectively. The relative density (RD) and relative abundance (RA) of SSRs were 42-44.43/kb and 6.25-6.59/kb while for cSSRs this value ranged from 7.06-8.1/kb and 0.50-0.55/kb respectively. However, RA and RD were weakly correlate with genome size and incidence microsatellites. The mononucleotide repeats (54.55%) were prevalent over di- (33.22%), tri- (11.88%), tetra- (0.27%), penta- (0.02%), hexanucleotide (0.04%) repeats, with poly (A/T) richness over poly (G/C). Motif composition of cSSRs revealed that maximum cSSRs were made up of two microsatellites having unique duplication pattern such as AT-x-AT, CG-x-CG. More numbers microsatellites represented within the coding region provides an insight into the genome plasticity that may interfere for gene regulation to mitigate with host-pathogen interaction and evolution of the species.

genomics↗

bioRxiv2021

Nickel-Sulfonate Mode of Substrate Binding for Forward and Reverse Reactions of Methyl-SCoM Reductase Suggest a Radical Mechanism Involving Long Range Electron Transfer

Methyl-coenzyme M reductase (MCR) catalyzes both synthesis and anaerobic oxidation of methane (AOM). Its catalytic site contains Ni at the core of Cofactor F430. The Ni ion, in its low-valent Ni(I) state lights the fuse leading to homolysis of the C-S bond of methyl-coenzyme M (methyl-SCoM) to generate a methyl radical, which abstracts a hydrogen atom from Coenzyme B (HSCoB) to generate methane and the mixed disulfide CoMSSCoB. Direct reversal of this reaction activates methane to initiate anaerobic methane oxidation. Based on crystal structures, which reveal a Ni-thiol interaction between Ni(II)-MCR and inhibitor CoMSH, a Ni(I)-thioether complex with substrate methyl-SCoM has been transposed to canonical MCR mechanisms. Similarly, a Ni(I)-disulfide with CoMSSCoB is proposed for the reverse reaction. However, this Ni(I)-sulfur interaction poses a conundrum for the proposed hydrogen atom abstraction reaction because the >6 [A] distance between the thiol group of SCoB and the thiol of SCoM observed in the structures appears too long for such a reaction. Spectroscopic, kinetic, structural and computational studies described here establish that both methyl-SCoM and CoMSSCoB bind to the active Ni(I) state of MCR through their sulfonate groups, forming a hexacoordinate Ni(I)-N/O complex, not Ni(I)-S. These studies rule out direct Ni(I)-sulfur interactions in both substrate-bound states. As a solution to the mechanistic conundrum, we propose that both forward and reverse MCR reactions emanate through long-range electron transfer from Ni(I)-sulfonate complexes with methyl-SCoM or CoMSSCoB, respectively.

biochemistry↗